Federation Queries

Ontul supports federated queries across multiple data sources through its multi-catalog architecture powered by Apache Calcite.

Multi-Catalog Architecture

Ontul uses a 3-level schema hierarchy for table resolution:

catalog.schema.table

Each catalog represents a separate data source. Multiple catalogs can be registered simultaneously, and a single SQL query can reference tables from different catalogs.

Cross-Source Joins

Join data across different data sources in a single query:

SELECT c.name, o.total
FROM jdbc_catalog.public.customers c
INNER JOIN iceberg_catalog.sales.orders o
  ON c.id = o.customer_id
WHERE o.status = 'completed';

In this example, customers comes from a JDBC database and orders comes from an Iceberg table — Ontul handles the distributed execution transparently.

Supported Catalog Types

Catalog Type	Description
Iceberg	REST catalog (e.g., Polaris, Nessie) for Iceberg tables
JDBC	Any relational database accessible via JDBC
TPC-H / TPC-DS	Built-in benchmark data

Dynamic Registration

Catalogs are registered at runtime through the Admin API or Admin UI. No cluster restart is required. Once registered, all tables within the catalog are immediately discoverable and queryable.

Schema Introspection

Standard metadata commands work across all catalog types:

SHOW CATALOGS;
SHOW SCHEMAS FROM my_catalog;
SHOW TABLES FROM my_catalog.my_schema;
DESCRIBE my_catalog.my_schema.my_table;

Ontul also provides information_schema virtual tables (tables, columns, schemata) for programmatic introspection.